Data security for digital data storage

ABSTRACT

A computing system includes data encryption in the data path between a data source and data storage devices. The data encryption may utilize a key which is derived at least in part from an identification code stored in a non-volatile memory. The key may also be derived at least in part from user input to the computer.

RELATED APPLICATION

This application is related to U.S. patent application Ser. No.09/277,335, titled “DATA SECURITY FOR DIGITAL DATA STORAGE,” filed Mar.26, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to methods and apparatus for providing securityfor digital data stored on data storage media such as magnetic andoptical disks and tapes.

2. Description of the Related Art

Over the past several years, personal computing systems have become morepowerful, smaller, and less expensive. As this has occurred, more andmore computing applications are performed on personal computerplatforms. Local and wide area networks of personal computers are nowoften used in corporate and business applications instead of the largemainframes used for the same applications in the past. A further resultof the increases in performance and decreases in price of personalcomputers is a dramatic increase in personal computer use for householdfinancial and other sensitive and preferably confidential information.

The use of personal computers in these applications raises data securityand privacy issues which have thus far been insufficiently resolved.Laptop and other personal computers, as well as the removable datastorage media used in them are transported, mislaid, lost, and sometimesstolen. Consequently, security and privacy issues which were not presentwhen computers and their data storage media were generally fixed havenow become prominent. Administrators of computer resources in thebusiness environment must remain aware of the location of portablecomputing devices as well as the nature of the programs and data storedon them. For home users, concerns arise if credit card, social security,or bank account numbers are present on fixed or removable media whichmay be lost or stolen.

To resolve a few of these concerns, some programs allow the user topassword protect documents or files, thereby preventing access to thedata in the file unless the password is known. This provides limitedsecurity, however, since these schemes are easy to defeat with widelyavailable password extraction programs. Furthermore, although the act ofopening the file may be restricted in the relevant application program,the data itself resides on the media in raw form, and may still beextracted by a trained computer user.

Systems have also been proposed which perform encryption on data andapplication programs stored on tape and disk. These systems provideimproved security over the password protection described above. As oneexample, a system disclosed in U.S. Pat. No. 5,325,430 to Smyth et al.(incorporated herein by reference in its entirety) includes a securitymodule attached to a personal computer which performs data andapplication program encryption. The security module communicates with aremovable smart card assigned to a given user which contains encryptionkeys used by the security module. Although the security provided by thissystem is adequate for many applications, the circuitry used toimplement the system is complex, and administration of the system forproducing and assigning keys and smart cards is time consuming andexpensive.

Another system for encrypting files is disclosed in U.S. Pat. No.5,235,641 to Nozawa et al., the disclosure of which is also incorporatedherein by reference in its entirety. In this system, data stored to amagnetic tape is encrypted by a cryptographic adapter which is locatedin the data path between a host processor and a tape drive. In thissystem, the host processor generates cryptographic keys which are storedon the tape itself. This requires additional logic to encrypt the keysas well as the data, and consequently, this system requires relativelycomplex circuitry, and leaves the key potentially recoverable from thetape itself if the key encryption scheme is broken.

Thus, existing encryption systems for personal and portable computershave serious drawbacks, and have not been widely implemented. Inparticular, a system which is useful for an individual personal computeruser has not been heretofore provided. Such a system should provide datasecurity with flexibility and without expensive administration orimplementation.

SUMMARY OF THE INVENTION

In a first embodiment, the invention includes a computing apparatuscomprising a digital data storage device and a logic circuit configuredto receive digital data and to forward the digital data to the digitaldata storage device in an encrypted form. The computing apparatus mayalso comprise a non-volatile memory location which stores anidentification code, as well as a second memory location coupled to thelogic circuit which stores an encryption key accessed by the logiccircuit derived at least in part from the identification code.

Another embodiment of the invention includes a circuit for encryptingdata in a computing system. The circuit may comprise a first memorylocation storing an identification code, and a logic circuit comprisinga second memory location and an encryption engine. The logic circuit maybe configured to receive the identification code and to store a key foruse by the encryption engine derived at least in part from theidentification code in the second memory location.

The invention also comprises a computer having a plurality of datastorage media drives and a data path connected between a source of dataand the data storage media drives. The computer may further include alogic circuit coupled to the data path which is configurable to enableencrypting of data being routed to a selectable subset of the pluralityof data storage media drives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a data storage system incorporating anembodiment of the invention.

FIG. 2 is a flow chart illustrating acts performed during key generationin an embodiment of the invention.

FIG. 3 is a block diagram illustrating an encrypting data path passingfrom a host processor to data storage devices, in accordance with oneembodiment of the invention.

FIG. 4 is a flow chart illustrating acts performed during key generationin another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described with reference to theaccompanying Figures, wherein like numerals refer to like elementsthroughout. The terminology used in the description presented herein isnot intended to be interpreted in any limited or restrictive manner,simply because it is being utilized in conjunction with a detaileddescription of certain specific embodiments of the invention.Furthermore, embodiments of the invention may include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the invention hereindescribed.

Referring now to FIG. 1, a data storage system is illustrated whichincorporates aspects of the invention. The system includesencryption/decryption logic 10 that is connected to receive digital datafrom a data bus 12. The encryption/decryption logic 10 is configured toforward data received from the data bus 12 to data storage devices 14 inan encrypted form. The data or information transferred between the databus 12 and the data storage devices may comprise application programsthemselves, data used by application programs, or any other informationthat the host computing system stores to the data storage devices 14 ofthe system. As will be further explained below with reference to FIGS. 2and 3, the encryption/decryption logic may in some embodiments beconfigurable to perform the encryption and decryption on a selectablesubset of the data storage devices if desired by a user of the system.

The algorithm used to perform the encryption may comprise any knownencryption algorithm, and many different alternatives will be well knownto those of skill in the art. In many applications, the encryption anddecryption process will be defined in part by a key 16 which is utilizedby the encryption/decryption logic 10 to perform the data manipulationwhich results in data encryption and decryption. In some systems, thesame key is used for both the encryption and decryption processes, butin others, the key 16 may comprise a pair of keys, wherein one is usedfor encryption, and the other for decryption. Given the variety ofencryption and decryption schemes which have been and are currentlybeing developed, the use of the word “key” is intended to encompass anypiece of information, data, parameter, definition, configuration oflogic circuitry, or other entity or circuit arrangement which serves atleast in part to configure the encryption/decryption logic, or tootherwise in any way partly or wholly define the data encryption processwhich is performed by the encryption decryption logic 10.

Also provided in the system of FIG. 1 is a non-volatile memory location18. As is well known in the art, a non-volatile memory has the propertythat the data or information stored in it remains when the host systemis powered down. Non-volatile memory may comprise battery backed up RAM,EPROM, EEPROM, or ROM memory circuitry, for example. In the applicationof FIG. 1, this memory location 18 may advantageously store anidentification code. The stored identification code may be used toderive, at least in part, the key 16 which is used in the encryptionprocess. This derivation may involve simply making the key theidentification code itself, or may alternatively involve a logical ormathematical manipulation or transformation of the identification codeto produce the key. In some embodiments, as will be further explainedbelow, the key 16 may be derived in part from the identification codestored in the non-volatile memory and in part from a password or otherpiece of information entered by a user of the computing system.

The system of FIG. 1 includes many advantages over prior art dataencryption schemes and is especially applicable to individual personalcomputer and laptop computer users. In some embodiments, the circuitryof FIG. 1 may be incorporated into, for example, a laptop computer whichis sold to an individual for household and/or business use. In most ofthese situations, the purchased computer will not be a member of a groupof computers which is controlled or overseen by a system administratorthat will create and assign encryption keys, smart cards, etc. Rather,the laptop will be simply used as is, for both personal and business useby a user who is generally unfamiliar with data security techniques orprocedures.

In these embodiments, the identification code may comprise a multi-bitdata word which is associated with the individual laptop being used.When stored in a non-erasable memory element such as ROM or EPROM, theidentification code may be substantially permanently associated with theindividual laptop being used. It will be appreciated that data securityin these environments is enhanced if different laptops do not typicallyshare a common identification code. When this is true, the key 16derived from the identification code will be different in differentlaptops produced by the laptop manufacturer. It will therefore also beappreciated that the data stored on the data storage devices 14 will beencrypted differently by different laptops. Thus, a removable media suchas a floppy disk, tape, or writeable CD will not be useable on anycomputer except the one that originally stored the data. Thus, a levelof security is provided for removable media which may be lost, mislaid,or stolen.

It will also be appreciated that this level of security is providedwithout any intervention by the user or a system administrator. Keygeneration and data encryption is automatic and transparent. Inaddition, this data security scheme is easily implemented in the largescale production of laptops and other personal computers. Machinespecific data encryption may be provided with the simple provision ofnon-volatile storage of information which defines the data encryptionprocess performed. This information may advantageously be substantiallyuniquely associated with the host computing logic or host computer. Thismay be ensured by using some form of sequential numbering scheme for theidentification code, or alternatively a random or pseudo-randomnumbering scheme with a low probability of producing two identicalidentification codes for different laptops. However, it may be notedthat it is not necessary to absolutely guarantee that each laptop have auniquely defined encryption process. The desirable feature is that therebe a relatively low probability that lost or stolen media will bereadable in some other laptop or personal computer available to someonewho has found or has stolen the media elements. Therefore, duplicateidentification codes and keys defining identical encryption processesmay be provided within a given set of computers while still maintaininga useful level of security. Thus, the association between identificationcodes and their respective host computers need only be substantiallyunique such that a reasonable level of security is created.

FIG. 2 illustrates a method of key generation and data encryptionaccording to one embodiment of the invention. It will be appreciatedthat the method shown in FIG. 2 may, in one embodiment, be implementedon hardware illustrated in FIG. 1.

The method begins at a start state 22, and moves from there to step 24,where an identification code is retrieved. The identification code maybe stored in a non-volatile memory, and may in addition be substantiallyuniquely associated with specific host computer hardware.

The system then moves to decision state 26, where it is decided whetheror not some user input should be utilized in the process of encryptionkey generation. If not, the method moves directly to step 28, where anencryption key is generated using the identification code retrieved atstep 24. If user input is to be used in key generation, the method movesfrom step 26 to step 30, where the user input is accepted by the system.The user input may, for example, comprise an alphanumeric code which istyped into the computer keyboard by the user in response to a systemprompt. Following this, the method moves to step 28, where the key isgenerated using both the identification code and the user input. Theuser input from step 30 may be an alphanumeric sequence which isconverted to a multi-bit word (for example, to ASCII code). This wordmay be combined with the identification code in many ways, includingconcatenation as one simple example, or other more complicated logicalor mathematical manipulations may be used.

Following key generation at step 28, the key is used to encrypt anddecrypt data that is stored to and retrieved from a data storage deviceat step 32. In the personal computer or laptop computer context, theseries of steps leading to and including key generation may be performedduring the boot operation prior to any accesses to encrypted datastorage devices. In these embodiments, all data, programs, etc. storedon the data storage devices are encrypted with the same key, a key whichmay require some user input to generate as described above. The computermay be either factory configured or user configured to require or notrequire user input for key generation.

The addition of user input to key generation provides an enhancement todata security beyond that provided when only the identification code isused to derive an encryption key. This is because if the entire computeris lost or stolen, when the computer is turned on only the computerowner will know what code or password to input in order to generate theproper key at step 28 of FIG. 2. Thus, access to encrypted programs anddata is effectively prevented even with the original computer the handsof an unauthorized user.

An embodiment of the invention is also illustrated in FIG. 3 which maybe used to implement the process described above with reference to FIG.2. In this Figure, a computer system is shown having a host processor36, which may, for example, comprise a member of the Pentium® family ofprocessors such as the Pentium, Pentium Pro, or Pentium II. Althoughindustry standard PC architecture is used as an illustrative example inthis Figure, it will be appreciated that many computer designs may beimplemented using the principles illustrated herein. Also provided aspart of the computer system of FIG. 3 are a plurality of data storagedevices, including hard disk drives 38, 40, a floppy disk drive 42 and aCD drive 46, which may be of a writeable type.

The processor 36 interfaces with a host bus 44 which also interfaceswith a bridge circuit 46. The bridge circuit 46 routes data from thehost bus 44 to a PCI bus 48. The PCI bus 48 provides a data source to alogic circuit 50 which is provided in the data path between the PCI bus48 and an IDE bus 52 and floppy drive control bus 54 which interfacedirectly with the respective data storage devices 38, 40, 42, 44, and46. The PCI bus 48 may also receive data from I/O devices 56 via a PCIto ISA bridge circuit 58.

The logic circuit 50 advantageously includes an encryption engine 60which operates to encrypt data routed to one or more of the data storagedevices 38, 40, 42, 46 and to decrypt data routed from one or more ofthe data storage devices 38, 40, 42, 46. The logic circuit 50 will alsogenerally include input and output bridge circuitry 51 to buffer dataand convert the data transfer protocol from the PCI format bus 48 to thebusses 52, 54, which interface directly with the data storage devices38, 40, 42, 46.

The encryption engine operates under the control of control logic 62.The control logic, in turn, receives information for controlling theencryption engine from three sources. The first is a memory locationwhich stores a hardware identifier 64. As described above, this hardwareidentifier 64 may be substantially uniquely associated with the computerhardware. The memory may comprise a non-volatile writeable or read onlymemory to help ensure essentially permanent storage of the hardwareidentifier 64. As is also described above, the hardware identifier 64stored in the memory may be used by the control logic 62 (oralternatively the processor 36) to at least in part derive a key forencryption and decryption of data to and from the data storage devices38, 40, 42, 46. The control logic may also accept user input asdescribed above to be used as additional information for key derivation.

This generated key may be stored in a key register 66 which also iscoupled to the control logic 62. Prior to data being stored or retrievedfrom the data storage devices 38, 40, 42, 46, the key may be retrievedfrom the key register 66 for use by the encryption engine 60 during theencryption and decryption processes.

A configuration register 70 may also be coupled to the control logic 62.The content of the configuration register 70 may advantageously be userdefined, and may include bits that determine which of the data storagedevices 38, 40, 42, 46 have data encrypted before storage to the media,and which have data decrypted when data is retrieved from the media.This feature provides significant flexibility to the user. A user may,for example, want to encrypt some, but not all, data stored onto afloppy disk with the floppy drive 42. It may also be advantageous tohave at least one hard drive 38 or 40, which contains DOS, Windows™,Unix™ or other operating system software, to remain unencrypted.

The configuration register may also contain bits which determine whetheror not user input should be incorporated into the key being used toperform the encryption and decryption. In some embodiments, a differentkey may be stored for different drives. In this case, some of the keysmay be generated with user input, and some without.

One advantageous aspect of the encryption system described herein isthat it may be created with relatively minor modifications to currentlyexisting integrated circuits. PCI to ISA and PCI to IDE bridges are wellknown and understood, and are commercially available from, for example,Intel Corporation. In one embodiment, therefore, an encryption engine,control logic, a key register, and a configuration register may beincorporated into an existing bridge integrated circuit design toproduce a portion of the logic circuit 50. Furthermore, individualEPROM, EEPROM and ROM memories which include pre-programmedidentification codes are available commercially from DallasSemiconductor of Dallas Tex. as part numbers DS2401 and DS2430 forexample. These devices include a unique 48 bit serial number in a ROMstorage location which may be utilized as the memory location whichstores the hardware identifier 64. These memory chips are available witha serial I/O interface for reading the identification code and any otherstored data. In this embodiment, therefore, a bridge integrated circuitwhich includes the encryption logic may interface over a serial bus to aseparate memory integrated circuit which stores the hardware identifier.

FIG. 4 illustrates a method of key generation and verification which maybe implemented with the system illustrated in FIG. 3. In the method ofFIG. 4, the control logic 62 (FIG. 3) may be utilized to perform keygeneration and verification without intervention by the processor 36(FIG. 3). The method begins at a start state 76. Following this startblock 76, the system retrieves the hardware identifier 64 (FIG. 3) fromthe non-volatile memory location where it is stored. This retrievalprocess may involve the sequential retrieval of a set of data words fromthe memory as illustrated by the loop defined by blocks 78, 80, and 82.Thus, at block 78, the control logic 62 may output an initial address tothe non-volatile memory to retrieve a first data word comprising aportion of the hardware identifier code 64. The address may then beincremented at block 80. If, at decision block 82, it is determined thatthe entire code has not yet been retrieved, the system loops back toblock 78 and outputs the incremented address to the non-volatile memoryto retrieve another segment of the code.

Once the entire code has been retrieved, at block 84 the control logic62 may then generate and verify the key. As mentioned above, the processof key generation may involve merely storing a concatenation of the datawords retrieved at steps 78-82 in the key register 66. This could occurduring the retrieval process, or afterwards. Alternatively, mathematicalor logical manipulations may be performed on the retrieved data wordsprior to their storage into the key register. Key verification may alsobe performed in a number of ways known to those of skill in the art. Forexample, a checksum or CRC field may be provided in the configurationregister 70 or control logic 62. If no user input is utilized in keygeneration, this field may be generated during an initializationsequence performed during the manufacture of either the logic circuit 50or a computer system that the logic circuit 50 is incorporated into. Ifuser input is utilized in key generation, this CRC or checksum field maybe generated during a password initialization routine when the passwordto be utilized in key generation is initially entered by the user.

Following key generation and verification, the system moves to adecision state 86, where the result of the key verification of block 84is checked. If the key is verified as good, the system moves to block88, and the key is used to encrypt and decrypt data during data storageand retrieval operations. There are several reasons why key verificationmight fail. An error in reading the hardware identifier may cause faultykey generation. Tampering with the logic circuit 50 may also result inincorrect key generation. Additionally, key verification may failbecause required operator input to be used in key generation has not yetbeen entered by a user. Thus, a failure of key verification may forceuser input. This is illustrated in FIG. 4 by the fact that if, atdecision state 86, the key has not been verified as good, the systemmoves to a another decision state 90. At decision state 90, the systemdetermines whether or not user input should be accepted and used in thekey generation process. If the system determines that operator inputshould be accepted, the system moves to block 92, where the input isread. The system then loops back to block 84, where the key is generatedusing both the operator input and the retrieved identification code, andis again verified against the stored CRC or checksum field. If theoperator input was the correct password, the key will be verified asgood at the next iteration of decision block 86, and at block 88, thekey will be used to encrypt and decrypt data as described above.

If, however, the operator input was incorrect, the key verificationprocess will fail, and the system will again move to decision state 90,where the system again determines whether or not user input should beaccepted. It will be appreciated that the user may be given two or moreattempts to successfully input the proper password. Thus, the system mayloop back to blocks 92 and 84 a plurality of times, any one of which mayresult in correct password entry and normal data encryption anddecryption at block 88.

After a selected number of iterations of incorrect password entry, thesystem may decide at state 90 to refuse to accept further operator inputfor key generation. In this event, the system moves to block 94 wherethe key error is flagged by the system. System response to the errorflag may vary widely. The system may indicate to the user that thepassword entries are incorrect. The system may even be programmed todestroy the content of encrypted drives in the event the keyverification process fails, or fails for a selected number ofconsecutive verification attempts.

The encryption system described thus provides data security to personaland laptop computer users in a transparent manner without requiring timeconsuming and expensive system administration or complex and expensivehardware. The system is especially adapted to individual users, and thehigh volume production of computers for these users.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention can be practiced in many ways.As is also stated above, it should be noted that the use of particularterminology when describing certain features or aspects of the inventionshould not be taken to imply that the terminology is being re-definedherein to be restricted to including any specific characteristics of thefeatures or aspects of the invention with which that terminology isassociated. The scope of the invention should therefore be construed inaccordance with the appended claims and any equivalents

1. A computing apparatus comprising: a digital data storage device; abus-to-bus bridge configured to receive digital data from a hostprocessor and to forward said digital data to said digital data storagedevice in an encrypted form, wherein said bus-to-bus bridge isconfigured to encrypt said digital data and forward the digital data tothe digital storage device without intervention of the host processor,and wherein a configuration register in the bus-to-bus bridge is adaptedto store information that is used by the bus-to-bus bridge toselectively enable and disable encryption depending on the target devicethat is to receive the data that is transmitted via the bus-to-busbridge; a non-volatile memory location in or connected to saidbus-to-bus bridge which stores an identification code; and a keyaccessed by said bus-to-bus bridge to define at least in part anencryption process, wherein said key is derived at least in part fromsaid identification code.
 2. The computing apparatus of claim 1, whereinsaid identification code is assigned to and associated specifically withsaid computing apparatus.
 3. The computing apparatus of claim 2, whereinsaid bus-to-bus-bridge is configured to verify said key withoutintervention by said host processor.
 4. The computing apparatus of claim1, wherein said bus-to-bus bus bridge additionally comprises a circuitfor selectively disabling said logic circuit from encrypting saiddigital data.
 5. The computing apparatus of claim 1, wherein said key isderived in part from said identification code and in part from userinput.
 6. A computer comprising: a plurality of data storage mediadrives; a data path connected between said plurality of data storagemedia drives and a source of data for storage onto media associated withsaid data storage media drives; and a bus-to-bus bridge coupled to saiddata path, said bus-to-bus bridge being configurable to enableencrypting of data being routed to a selectable subset of said pluralityof data storage media drives, wherein said bus-to-bus bridge isconfigured to encrypt said digital data and forward said digital data tosaid data storage media drives without intervention of the hostprocessor, and wherein a configuration register in the bus-to-bus bridgeis adapted to store information that is used by the bus-to-bus bridge toselectively enable and disable encryption depending on the target devicethat is to receive the data that is transmitted via the bus-to-busbridge.
 7. The computer of claim 6, wherein said plurality of datastorage media drives includes one or more hard disk drives, and one ormore floppy disk drives.
 8. The computer of claim 6, wherein saidbus-to-bus bridge additionally comprises: a non-volatile memory locationwhich stores an identification code; and a second memory location whichstores an encryption key derived at least in part from saididentification code, wherein said key is accessed by said bus-to-busbridge to encrypt said digital data for storage on said data storagemedia drives.
 9. The computing apparatus of claim 8, wherein saididentification code is assigned to and associated specifically with saidcomputer.
 10. A data processing system comprising: a data source; atleast one data storage device; a logic circuit coupled to receivedigital data from said data source and to route digital data to saiddata storage device, wherein said logic circuit is configured to encryptsaid digital data and forward the digital data to the data storagedevice without intervention of a host processor, wherein the logiccircuit comprises a bus-to-bus bridge; a non-volatile memory coupled tosaid logic circuit with a serial data bus, said read only memorycontaining a hardware identifier; a key register coupled to said logiccircuit, said key register storing a key for performing data encryption,wherein said key is derived at least in part from said identificationcode; and a configuration register coupled to said logic circuit,wherein said configuration register contains information enabling saidlogic circuit to perform encryption on digital data received from saiddata source using said key prior to storing encrypted digital data onsaid at least one data storage device, and wherein the configurationregister is adapted to store information that is used by the logiccircuit to selectively enable and disable encryption depending on thetarget device that is to receive the data that is transmitted via thebus-to-bus bridge.
 11. The data processing device of claim 10, furthercomprising at least two data storage devices, wherein said configurationregister contains information enabling data encryption of data routed toa first one of said at least two data storage devices, and wherein saidconfiguration register contains information disabling data encryption ofdata routed to a second one of said at least two data storage devices.12. A circuit for encrypting data in a computing system comprising: afirst memory location storing an identification code; and a logiccircuit comprising a second memory location and an encryption engine,said logic circuit configured to receive said identification code fromsaid first memory location and to store a key for use by said encryptionengine, said key being derived at least in part from said identificationcode in said second memory location, wherein said logic circuit isconfigured to encrypt digital data and forward said digital data to adigital storage device without intervention of a processor, wherein thelogic circuit comprises a bus-to-bus bridge, and wherein a configurationregister in the bus-to-bus bridge is adapted to store information thatis used by the logic circuit to selectively enable and disableencryption depending on the target device that is to receive the datathat is transmitted via the bus-to-bus bridge.
 13. The circuit of claim12, wherein said first memory location resides on a first integratedcircuit, and wherein said logic circuit resides on a second integratedcircuit separate from said first integrated circuit.
 14. The circuit ofclaim 13, wherein said first and second integrated circuits are coupledby a serial data bus.
 15. A computer system comprising: host computinglogic, wherein said logic circuit is configured to encrypt digital dataand forward said digital data to a digital storage device withoutintervention of a host processor, wherein the host computing logic is abus-to-bus bridge, and wherein a configuration register in thebus-to-bus bridge is adapted to store information that is used by thelogic circuit to selectively enable and disable encryption depending onthe target device that is to receive the data that is transmitted viathe bus-to-bus bridge; means for storing an identification codeassociated with said host computing logic; and means for deriving a keyfor data encryption at least in part from said identification code. 16.The computer system of claim 15, wherein said means for deriving a keyadditionally comprises means for deriving a key at least in part fromuser input to said computer system.